Ejector device

ABSTRACT

An ejector device that includes one or more ejectors comprises an ejector layer that spans at least one hollow area. The ejector layer has a first surface and an opposing second surface arranged to receive a viscous material with viscosity between 20 and 50,000 centipoise. The ejector layer includes a radiation absorber material configured to thermally expand without phase transition in response to heating by activation radiation transmitted to the first surface. Thermal expansion of the ejector layer causes displacement of the ejector layer and ejection of the material from the second surface of the ejector layer.

RELATED PATENT DOCUMENTS

This application is a divisional of U.S. application Ser. No.16/524,830, filed Jul. 29, 2019, which is a divisional of U.S.application Ser. No. 14/576,159, filed Dec. 18, 2014, now U.S. Pat. No.10,363,731, to which priority is claimed and which are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

This disclosure relates generally to ejectors for printing, as well assystems that incorporate such ejectors and methods pertaining to suchejectors.

BACKGROUND

Three dimensional (3D) printing is a process of making three dimensionalsolid objects by ejecting ink toward a print surface. Typically anadditive process is used wherein layers of the object being formed aresuccessively printed and fused. The printing of 3D objects has thepotential to significantly lower risks and costs of manufacturing. Forexample, using 3D printing, prototyping expenses can be significantlyreduced and mass manufacturing of identical items is not necessary torecoup initial tooling startup investment. One interesting aspect of 3Dprinting is the formation of living tissue structures and organs usingbio-inks.

Some 3D printed objects involve the printing of viscous inks. Theseviscous inks, which include bio-inks, require ejectors capable ofefficiently printing viscous materials. In the case of bio-inks, theprinting process needs to avoid shearing of cells and/or extracellularmaterial.

SUMMARY

Various embodiments described herein involve systems, devices, andmethods for printing of high viscosity inks. Some embodiments involve anejector device configured to eject material having viscosity between 20and 50,000 centipoise. The ejector device includes one or more ejectorscomprising an ejector layer that spans a hollow area. The ejector layerincludes a first surface and an opposing second surface arranged toreceive the viscous material. The ejector layer includes a radiationabsorber material configured to thermally expand without phasetransition in response to heating by activation radiation transmitted tothe first surface. The thermal expansion of the ejector layer causesdisplacement of the ejector layer and ejection of the material from thesecond surface of the ejector layer.

The ejector device may include one or more ejectors arranged in anarray. For example, the array may include one or more hollow mesas orone or more hollow islands. In some embodiments, the ejector deviceincludes a substrate, one or more mesas disposed on the substrate whereat least one of the mesas is an ejector mesa comprising the ejectorlayer that spans the hollow area, and at least one channel disposedadjacent to at least one of the one or more mesas, the channel beingconfigured to carry the material to the ejectors. To facilitateactivation radiation reaching the ejector layer, the substrate maycomprise a material that is transparent at wavelengths of the activationradiation and/or one or more vias through the substrate.

In some embodiments, the ejectors comprise one or more hollow mesas,each of the one or more hollow mesas disposed between solid mesas. Theejector layer may include at least one layer that conforms to thechannel and walls of the solid mesas. A thermally conductive layer isdisposed at least partially along the channel. In some implementations,the substrate can include vias that fluidically couple the channel to asource of the ejectable material. An aperture layer may be disposed atleast partially over the channel.

The ejector layer may include multiple layers. In some configurationsthe multiple layers include a first layer having a first coefficient ofthermal expansion, CTE₁, and a second layer having a second coefficientof thermal expansion, CTE₂, wherein CTE₂>CTE₁. The absorption of theactivation radiation in the second layer causes the ejector layer tobuckle in some embodiments. For example, suitable materials for thesecond layer may comprise amorphous Ge or amorphous Si. In someconfigurations, the ejector layer may include a layer that comprises abinding material configured to provide a predetermined surface energy.

The ejector layer may be relatively flat or may be curved. For example,in some embodiments a portion of the ejector layer over the hollow areais convex and bends toward the substrate. In some implementations, theejector layer can be formed so that it has a built in stress gradient.

Some embodiments involve a system that includes an ejector device asdiscussed above in addition to a radiation source configured to providethe activation radiation to the one or more ejectors, a fluidicssubsystem configured to carry the material to the at least one channel,a transport subsystem configured to provide relative movement betweenthe ejector device and the media surface.

Some embodiments are directed to a method of ejecting material. Adroplet of viscous material is disposed on an ejector, the ejectorincluding an ejector layer having a first surface and an opposing secondsurface arranged to receive the droplet of material. The ejector layeris heated by activation radiation. The heating causes the ejector layerto thermally expand without phase transition. In response to the thermalexpansion of the ejector layer, the material is ejected from the secondsurface.

Some embodiments involve a method of making an ejector device. A basematerial is deposited on a substrate and is patterned to form one ormore sacrificial regions. At least the sacrificial region is conformallycoated with an ejector layer. The sacrificial region is etched to forman ejector comprising the ejector layer spanning a hollow area. Theejector layer is configured to thermally expand without phase transitionin response to heating by activation radiation. The thermal expansion ofthe ejector layer causes ejection of a droplet from the ejector layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross sectional view of an ejector device taken throughplane A-A′ in accordance with some embodiments;

FIG. 1B is a plan view of the ejector device of FIG. 1A;

FIGS. 1C and 1D are alternative configurations of an ejector devicetaken through plane A″-A in accordance with some embodiments;

FIG. 2 is a plan view of an ejector device that includes a twodimensional array of island ejectors;

FIGS. 3A-3C illustrate various ways the ejector layer can be heated by aactivation radiation;

FIG. 3D illustrates an ejector device that includes a stop feature inaccordance with some embodiments;

FIGS. 4A-4B illustrate convex and concave ejector surfaces,respectively, in accordance with various embodiments;

FIGS. 4C-4E illustrate thermal expansion of an initially convex ejectorlayer in accordance with some embodiments;

FIGS. 5 and 6 provide cross sectional views of portions ejection devicesaccording to various aspects;

FIG. 7A is a cross sectional view of an ejector device the includessupport structures in accordance with some embodiments;

FIG. 7B is a plan view of the ejector device of FIG. 7A;

FIGS. 8A-8D illustrate ejection of a droplet of ejectable material fromthe free surface of an ejector layer;

FIGS. 9A-9C illustrate an ejector device in accordance with someembodiments;

FIGS. 10A-10I illustrate a process of fabricating an ejector device inaccordance with some embodiments;

FIGS. 11A-11D illustrate a process of fabricating an ejector devicehaving an ejector mesa with surface features in accordance with someembodiments;

FIGS. 12A-121 illustrate a process of fabricating an ejector devicehaving an ejector mesa with built in convexity in accordance with someembodiments;

FIG. 13 is an ejector system in accordance with some embodiments; and

FIG. 14 is a flow diagram illustrating an ejection process.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DESCRIPTION

There are many applications in which inks having high viscosity, e.g.,between about 20 centipoise and 50,000 centipoise need to be patternedwith precision, optionally in a 3D configuration. Although there aremany such applications, one of particular interest is the patterning of“bio-inks” comprising biologically active components (such as livecells, extracellular matrix materials, etc.). Embodiments disclosedherein relate to devices, systems, and methods for printing by ejectingdroplets of ejectable material, including high viscosity inks. Theapproaches discussed can be particularly useful for 3D printing ofbio-inks with reduced shearing of cells and/or extracellular materials.

FIGS. 1A and 1B respectively show cross sectional (through plane A-A′ ofFIG. 1B) and plan views of an ejector device 100 that includes one ormore ejectors 101. As best seen in FIG. 1B, the ejectors 101 in theillustrated embodiment are arranged in a row 199 forming a onedimensional ejector array. Alternatively, in some embodiments theejectors can be arranged in multiple rows and/or in other patterns thatform a two dimensional ejector device.

As best seen in FIG. 1A, each ejector 101 comprises an area of anejector layer 110 that is suspended over a hollow area 125 locatedbetween the ejector layer 110 and a substrate 150 that forms a hollow orpartially hollow ejector mesa 175. As discussed in more detail below,the suspended ejector layer 110 of the ejector mesa 175 can be formed byconformally coating the ejector layer 110 over sacrificial supportmaterial and then etching some, most, or all of the sacrificial supportmaterial.

In some embodiments, as shown in FIG. 1D in a cross section takenthrough plane A″-A′″ of FIG. 1B, the sacrificial support material usedto form the hollow area 125 may be substantially or completely etchedaway. In these embodiments, the hollow area 125 is an elongated areathat extends substantially the entire length of the ejector mesa 175.The ejectors 101 a, 101 b, 101 c are localized regions along the ejectorlayer 110.

In some embodiments, as shown in FIG. 1C in a cross section takenthrough plane A″-A′″, portions of the support material 171 may remainafter etching. The ejector mesa may include multiple hollow areas 125a-c, each hollow area 125 a-c being surrounded by support material 171.In the embodiment illustrated in FIG. 1C, one hollow area corresponds toone ejector 101 a-c.

The ejector layer 110 may be a single layer unimorph ejector layer or amultimorph ejector layer comprising multiple layers. The ejector layer110 has a first surface 121 that faces the substrate 150 and an opposingsecond surface 122 arranged to receive ejectable material 165, e.g., aviscous ink such as a bio-ink. At least one of the layers of the ejectorlayer 110 is configured to thermally expand without a phase transitionin response to heating by activation radiation 198, e.g., pulsed laserlight. Thus, the ejection of the ejectable material 165 from the ejectorlayer 110 substantially occurs due to thermal expansion of the ejectorlayer, and does not substantially occur due to phase transition of theejector layer from one form of matter to another form of matter as inthe laser induced forward transfer (LIFT). The LIFT printing techniquerelies on phase conversion of the ejector layer from liquid or gel formto gaseous form. In the embodiments described herein, thermal expansionof at least one layer of the ejector layer 110 causes the ejector layerto deflect with sufficient acceleration to eject the ejectable material165 from the second surface 122 of the ejector layer 110.

In some configurations, the ejector device 100 may include mesas 170disposed on one or both sides of the ejector mesa 175. In theillustrated embodiment, the ejector device 100 includes one or morechannels 180 formed by the mesa walls 170 a, 175 a and the region 151between the mesa walls 170 a, 175 a. The mesas 170 can comprise the samematerial as the sacrificial material used to make the ejector mesa 175and may not have hollow areas. One or more layers of ejector layer 110may conformally coat the mesas 170 and regions 151 of channel 180.

Channels 180 may be arranged to carry the ejectable material to theejectors 101. To fill the ejectors, the ejectable material can be causedto flow through the channels 180 and over the second surface 122 of theejector layer 110 and subsequently to recede, leaving droplets 165 ofthe ejectable material on the second surface 122. For example, theejectable material may be pressurized, causing the ejectable material toflow over the second surface 122, and then depressurized, causing theejectable material to recede. An aperture structure 190 that at leastpartially covers the channels 180 may be used to facilitate retention ofthe ejectable material in the channels 180 during the filling processand reduce evaporation or contamination of the ejectable material duringuse.

The implementations illustrated in FIGS. 1A through 1D compriseelongated mesas and ejector mesas 170, 175, wherein ejector mesa 175includes one or more hollow areas 125 associated with multiple ejectors101. Alternatively, in some configurations, an ejector device 200 mayinclude a one or two dimensional array of islands 270, as illustrated inplan view in FIG. 2. Some or all of the islands 270 include ejectors 201associated with hollow areas 225 surrounded by island support material271. The ejector layer 210 is suspended across the hollow areas 225 andone or more ejector layers may be disposed over the island walls and/orover the surface of the substrate 250 in the region 251 between theislands 270. The island walls 270 a and surface 251 of the substrate 250form channels 280 through which the ejectable material can flow to formdroplets 165 preferentially on the ejectors 201.

As illustrated in FIGS. 3A and 3B, heating of the ejector layer 310 mayoccur due to laser light 399 that is transmitted through a substrate 360that is transparent to the laser light and through hollow area 325(which may be an air gap). In these configurations, the laser light 399is first incident on the first surface 311 of the ejector layer 310.

In some configurations, as shown in FIG. 3B, the substrate 362 need notbe substantially transparent to the laser light 399. The laser light isdirected through one or more vias 361 formed through the substrate 362.The laser light 399 travels through the vias 361, through the hollowarea 325 and first encounters the ejector layer 310 at the first surface311 of the ejector layer 310. In some implementations, as shown in FIG.3C, the laser may be positioned so that the laser light 399 firstencounters the ejector layer 310 at the second surface 312 of theejector layer 310.

As previously discussed, the ejector layer may be a single layerunimorph or a multimorph comprising multiple layers. When heated by thelaser light, thermal expansion causes the unimorph or multimorph ejectorlayer to thermally expand, the thermal expansion resulting in an out ofplane displacement of the ejector layer, e.g., along the +z axisindicated in FIG. 1A. The displacement caused by thermal expansion maybe a relatively continuous displacement or may be a sudden displacementdue to buckling of the ejector layer. For example, as discussed in moredetail below, Euler buckling and snap buckling are two bucklingphenomena that may lead to buckling of the ejector layer due to thermalexpansion. Buckling displaces the ejector layer over a shorter period oftime leading to higher acceleration of the ejector layer when comparedto continuous displacement of the ejector layer.

For highly absorbing layers the incident laser radiation is morestrongly absorbed near the surface of incidence. The exponentiallydecreasing level of radiation leads to greater heating and concomitantthermal expansion nearest the surface of incidence of the excitationlight. Thus, even in a unimorph ejector, a bias exists which breaks theout of plane symmetry and biases the structure for buckling towards thesurface of incidence. Furthermore, a unimorph ejector layer having asingle layer can exhibit more directional variability in the buckling ofthe ejector layer when compared to the directional determinism ofbuckling bimorph or multimorph ejector layers. In some implementationsthe ejector layer may have certain features or properties that cause theejector layer to deflect in a particular direction. For example, theejector layer may include features on one or both of the first andsecond surfaces, e.g., corrugation features or puckers, that bias thedeflection in a particular direction. Alternatively or additionally, theejector device may optionally include one or more stop features thatlimit the deflection of the ejector layer in some directions, e.g., the−z direction, as shown in FIG. 3D. FIG. 3D illustrates a stop feature340 disposed within the hollow area 325 to limit the displacement of theejector layer 310 in the −z direction. The one or more stop featureswithin the hollow area may comprise a number of cylinders, a narrow mesaand/or a tapered mesa supported by the substrate 350. As shown in FIG.3D, the stop feature may be configured so that the activation light canbe focused within the stop feature.

As shown in FIGS. 4A and 4B, respectively, prior to heating and/orthermal expansion, a portion of the second surface of the ejector layer410, 420 may be a convex surface 412—curved toward the substrate 450 ormay be a concave surface 422—curved away from the substrate 450. Inconfigurations as illustrated in FIG. 4B that include a concave ejectorlayer surface 422, heating and thermal expansion may cause additionaldeflection of the ejector layer 422 in the direction of the concavity(positive z direction as shown in FIG. 4B).

In configurations as illustrated in FIG. 4A that include a convexejector layer surface 412, heating and thermal expansion may causeadditional deflection of the ejector layer 412 in the direction of theconvexity (negative z direction as shown in FIG. 4A), particularly ifthe ejector layer 410 is a unimorph.

In configurations that include a convex ejector layer surface 412, asillustrated in FIGS. 4C-4E, the deflection of the ejector layer 410 dueto thermal expansion may cause the ejector portion 412 of the ejectorlayer 410 to deflect from a convex −z position as shown in FIG. 4C,through a zero z position as shown in FIG. 4D, to a concave +z positionas shown in FIG. 4E. The illustrated deflection propels an ink dropletdisposed on the surface 412 toward the print surface with a “slingshot”type snapping deflection motion.

Zero stress, uniform stress or a stress gradient may be incorporatedinto one or more of the ejector layers by appropriately adjustingdeposition parameters used to deposit the layer such that no stress orunresolved lateral stresses are frozen into the layer. For example,where the ejector layer is deposited by sputtering, sputteringparameters such as sputtering rate and/or voltage, can be adjusted toform layers with zero stress, with uniform compressive or tensile stressor with a stress gradient.

In some implementations, the unimorph or multimorph ejector layer may beformed so that the ejector layer has no internal stress. Layers withzero internal stress may be substantially flat, or may be concave orconvex.

In some implementations, the unimorph or multimorph ejector layer may beformed so that one or more of the ejector layers have a uniform internalstress through the thickness of the layer along the z axis. The internalstress gradient causes the ejector layer to have a bias towarddeflection out of the xy plane in either the +z or −z direction. Whenlayers deposited with uniform tensile stress are released by etching ofthe sacrificial material, the ejector layer resembles a stiff drum head.Uniform compression may cause the ejector layer to deflect, e.g.,non-deterministically, or to resolve to a higher mode, e.g., formingwaves or corregations in the layer.

In some implementations, the unimorph or multimorph ejector layer may beformed to have a stress gradient along the z axis. For ejector layerformed with a stress gradient, the ejector layer may be designed forsnap buckling. Snap buckling may be able to achieve higher accelerationthan continuous deflection. Formation of a stress gradient in theejector layer can be implemented by forming a first portion of theejector layer proximate to the sacrificial material so that it is undercompressive stress and forming a second portion of the ejector layer onthe opposing side so that it is under no stress or tensile stress. Afterthe sacrificial material is removed, the first portion of the ejectorlayer proximate to the (now absent) sacrificial material is biased toexpand and the opposing second portion of the ejector layer is biased tocontract or not expand. These internal stresses cause the ejector layerto deflect slightly towards the −z direction to form a convexly dimpledmembrane as shown in FIG. 4C. When heated, by design the portion of theejector layer nearest the substrate expands more quickly than the upperportion of the ejector layer so that when thermal expansion occurs, theejector layer deflects through the midpoint (FIG. 4D) and continues todeflect in the +z direction (FIG. 4E) where the ejector layer is againat rest at a local stress minimum.

FIGS. 5-6 provide cross sectional views of various aspects of ejectordevices. FIG. 5 shows a portion of an ejector device that includes aunimorph ejector layer 510 in accordance with some embodiments. Aspreviously discussed, some implementations include a transparentsubstrate wherein the activation radiation is transmitted through thetransparent substrate 550, through the hollow area 525 and is initiallyincident on the first surface 521 of the unimorph ejector layer 510. Thethermal expansion of the layer 510 causes deflection of the layer 510and ejection of a droplet of the ejectable material (not shown in FIG.5) from the second surface 522 of the ejector layer 510. The deflectiondue to thermal expansion may be relatively continuous, or may be asudden deflection due to buckling.

The ejector layer 510 may include various monolayers that contribute tovarious characteristics of the ejector layer 510 such as opticalabsorption, antireflective properties, surface interfacial energy,and/or other characteristics. In implementations that include suchmonolayers, the ejector layer may still be referred to as a unimorphbecause the additional monolayers may be negligibly thick, are not undertensile or compressive stress in the plane of the ejector layer, and/ordo not significantly contribute to the mechanical response of theunimorph ejector layer to heating.

In some implementations, the ejector layer 510 optionally includes abinding layer 515 and/or surface treatment of the ejector layer. When abinding layer and/or surface treatment is included, the binding layerand/or surface treatment can be disposed in the region of the ejector,e.g., where the ejector layer 510 spans the hollow area 525 and mayextend over the walls of the ejector mesa and/or over the channelsurface. The binding layer and/or surface treatment may be designed toprovide a specified surface energy at the second surface 522 of theejector layer 510. The specified surface energy is selected to initiallyretain the ink droplet on the second surface 522 and then to allow forthe ejection of the ink droplet from the second surface 522 when theejector layer deflects. The surface energy of the second surface of theejector layer may provide for a contact angle with the ink of greaterthan 10 degrees, greater than 50 degrees, greater than 80 degrees, forexample, about 90 degrees or in the range of about 50 to about 100degrees.

Some types of ink, e.g., bio-inks are heat sensitive. At least one ofthe ejector layers may comprise a thermally resistive layer configuredto impede heat transfer to the ejectable material in the channel and/oron the ejector surface. The thermally resistive layer may have a thermalresistance (equal to thermal conductance x layer thickness) thatprovides heat transfer from the absorber layer of the ejector layer tothe ejectable material that is less than a specified value.

FIG. 6 illustrates in cross section a portion of an ejector device thatincludes a multimorph (bimorph) ejector layer 610 comprising multiplelayers 611, 612 that each contribute to the mechanical response toheating of the ejector layer 610. Each layer 611, 612 of the bimorphejector layer 610 can have a different thermal coefficient of expansion(CTE). In general, a thermal bimorph may include two or more than twolayers bonded together, one of the layers having a higher CTE than theother layer. When bimorph layers are deposited, the layer materials maybe at their equilibrium lengths and, if so, the bimorph will besubstantially flat as released from the sacrificial layer. When thetemperature of the bimorph increases, the layer having the higher CTEexpands more than the layer having the lower CTE. When heated, due tothe layers being bonded together, the high CTE material is stretchedbelow its equilibrium length and undergoes lateral compressive stressand the low CTE material is stretched above its equilibrium length andundergoes lateral tensile stress. The compressive stress of the higherCTE material and the tensile stress of the lower CTE material cause thebimorph to curl towards the lower CTE material to minimize the internalenergy stored by the stress.

The use of thermal bimorph layers can enable Euler buckling above astress threshold. Euler buckling in a bimorph occurs when the lateralcompressive stress in the bimorph layer having a higher coefficient ofthermal expansion becomes large enough for the buckled mode to lie atlower energy than the flat stressed layer. Deflection of the bimorphejector layer during buckling can provide much faster acceleration thanthe average rate of change of the stress, thereby effectively increasingthe momentum transfer to the droplet of ejectable material.

In some embodiments, the bimorph ejector layer 610 can include a firstlayer 611 that is substantially transparent to the activation radiationand a second layer 612 disposed over the first layer 611 that is highlyabsorbing to the activation radiation. In other embodiments, the bimorphejector layer 610 can include a first layer 611 that is highly absorbingto the activation radiation. In the latter case the thermalequilibration time constant between the sublayers needs to be short incomparison to the buckling time. The first layer 611 has a firstcoefficient of thermal expansion, CTE₁, and a second sublayer 412 has asecond coefficient of thermal expansion, CTE₂, wherein CTE₂>CTE₁.

The ejector layer 610 thermally expands without phase transition and maybuckle after a threshold stress is reached in the second sublayer 612 inresponse to heating by activation radiation which is transmitted throughthe substrate 650, through the hollow area 625 and absorbed in eitherthe first sublayer 611 and/or the second sublayer 612 of the ejectorlayer 610. Euler buckling of the bimorph layer 610 causes ejection of adroplet of the ejectable material (not shown in FIG. 6) from the secondsurface 622 of the ejector layer 610. Although not shown in FIG. 6, insome implementations, the bimorph may include additional monolayers,such as a binding layer and/or surface treatment of the ejector layer asdiscussed in connection with FIG. 5.

In some implementations, an ejector mesa 775 may include one or moresupport structures comprising support material 771, e.g., submesas 776as shown in FIGS. 7A and 7B. The support submesas 776 are adjacent andbonded to the ejector mesa 775. The cross sectional view of FIG. 7A istaken through plane B-B′ of FIG. 7B. The ejectors 701 include an ejectorlayer 710 that spans hollow area(s) 725 of ejector mesa 775 and alsocovers at least a portion of the tops of the support structures 776. Theejector layer 710 may optionally extend over the sides of the supportstructures 776, over the surface of the substrate 751, and/or over thetops of mesas 570. At least one of the layers of the ejector layer 710is configured to thermally expand without phase transition in responseto heating by activation radiation. Thermal expansion of the layer ofthe ejector layer 710 causes deflection of the ejector layer 710 andejection of the droplet from the ejector layer 710.

Mesas 770 may optionally be disposed on one or both sides of the ejectormesa 775. Channels 780 are formed by the mesa walls 776 a, 770 a and theregion 751 adjacent to and/or between the mesa walls 776 a, 770 a. Themesas 770 comprise mesa support material 771 without hollow area(s). Asshown in FIG. 7A, one or more sublayers of ejector layer 710 can be acontinuous layer that extends over the mesa support material 771 of thesupport structure(s) 776, spans the hollow area 725, extends over region751 of channel 780, and/or extends over the mesa support material 771 ofmesa(s) 770.

The channels 780 can be arranged to carry the ejectable material to theejectors 701. To fill the ejectors, the ejectable material can be causedto flow through the channels 780 and over the ejector surface 722 of theejector layer 710 and subsequently to recede, leaving droplets of theejectable material preferentially adhering to the ejector surface 722.An aperture structure 790 that at least partially covers the channels780 may be used to facilitate retention of the ejectable material in thechannels 780 during the filling process.

FIGS. 8A through 8D illustrate ejection of a droplet 865 of ejectablematerial from the free surface of an ejector layer 810. FIG. 8A showsthe droplet 865 and ejector layer 810 in its steady state condition attime to, prior to heating by the activation radiation.

FIG. 8B illustrates the ejector layer 810 and droplet 865 at time t₁,the point of maximum excursion of the ejector layer 810 from its steadystate condition by relatively constant deflection and/or buckling due tothermal expansion. The excursion of the layer 810 is maximum and thevelocity of the membrane 810, V_(membrane), due to thermal expansion iszero in FIG. 8B.

FIG. 8C shows the membrane 810 as it rebounds and cools and moves towardits steady state position with velocity V_(membrane). The droplet 865 ismoving away from the membrane 610 with a velocity V_(drop). The velocityof the droplet V_(drop) relative to the velocity of the membraneV_(membrane) must exceed a threshold velocity, V_(threshold), to detachfrom the surface of the membrane 610, where

${V_{threshold} = \left( \frac{2\gamma A}{m} \right)^{\frac{1}{2}}},$

where γ is the interfacial energy of the free surface of the ejectormembrane 810, A is the area of the droplet 865, and m is the mass of thedroplet 865. For example, where the ejector surface layer 810 ispolycarbonate having a surface energy of about 0.03 J/m², for a droplethaving a thickness of about 4 μm, an area of about 50 μm, and a mass ofabout 10¹¹ kg, V_(threshold)≈4 m/s.

FIG. 8D shows the droplet 865 after detachment from the ejector layer810. The ejector layer 810 has returned to its steady state position.

FIGS. 9A-9C illustrate an ejector device 900 in accordance with someembodiments. FIG. 9B is a plan view of the ejector device 900 and FIG.9A is a cross sectional view taken through plane C-C′. FIG. 9C shows across sectional view of layers of ejector layer 910. In someimplementations, one or more of the ejector layers may also partially orfully cover the mesa walls 970 a. The ejector 901 is formed with ahollow area 925 between the ejector layer 910 and the substrate 950. Theejector layer 910 includes layer 911 that is substantially transparentto the activation radiation. Layer 911 spans the hollow area(s) 925 ofejector mesa 975, the channel 980, and mesas 970. In the illustratedembodiment, layers 912, 913, 915 of the ejector layer 910 at leastpartially cover the hollow area 925. In other implementations, one ormore of sublayers 912, 913, 915 may optionally conformally cover thechannels 980 and/or mesas 970.

The ejector layer 910 is disposed on a substrate 950 wherein vias 955through the substrate fluidically connect the channels 980 with amanifold, reservoir or other structure (not shown in FIG. 9A) configuredto contain the ejectable material 965 such as a bio-ink. At least one ofthe sublayers of the ejector layer 910 is configured to thermally expandwithout phase transition in response to heating by activation radiation,e.g., laser light, which can be transmitted through a substrate 950substantially transparent to the laser light. The laser light istransmitted through the hollow area 925, and through the radiationtransparent layer 911. In some embodiments, the layers of the ejectorlayer 910 form a thermal bimorph configured to undergo Euler buckling.

As best illustrated by FIG. 9C, layers 911 and 912 form a thermalbimorph wherein layer 912 has a higher CTE than layer 911. In someembodiments, layer 913 is optionally present as a low modulus, highthermal expansion coefficient thermal insulator, such as silicone orpolycarbonate. In some embodiments, layer 915 is an optional additionalsurface energy presenting layer such that the droplet wetting angle is˜90 degrees. In some embodiments, layer 911 may be or comprise silicaand layer 912 may be or comprise amorphous germanium, amorphous silicon,or tungsten, for example. Some typical values for CTEs (×10⁻⁶ per degreecentigrade) are 0.6 for silica, 6 for silicon, 8 for amorphousgermanium, and 13 for tungsten. One or more of the ejector layers 912,913, 915 may extend to and/or may be patterned in the channel 980. Insome embodiments, a heat conducting layer such as copper may bepatterned in the channel and/or may extend up the walls of the mesas tohelp spread the heat after each laser pulse. The substrate 950 maycomprise a material that provides structural support for the ejectordevice and may be substantially transparent to the activation radiation.For example glass is a suitable material for the substrate 950. The mesamaterial may comprise silica, silicon oxynitride, silicone, etc.

Parameters for the layers of the ejector device can be varied to providefor ejection at a specified, e.g., minimum, laser energy input.Radiation power density of the activation light may be in a range ofabout 10 to 100 mW per ejector and pulse length range of about 0.1 to 10microseconds. Layer thicknesses for each layer may be in a range ofabout 1 to 100 microns. Ejector diameters of 10-100 microns with similarpitch are suitable for many embodiments of the ejector device.

Returning now to FIGS. 9A and 9B, in addition to at least one ejectormesa 975 spanning hollow area(s) 925, the ejector device 900 includesmesas 970. The mesas 970 may optionally be disposed on one or both sidesof ejector mesa 975. In the illustrated embodiment, the ejector device900 includes at least one channel 980 formed by the mesa walls 970 a,975 a and the region 951 between the mesa walls 970 a, 975 a.

As shown in FIG. 9A, one or more layers of ejector layer 910, mayconformally coat the region 951 of channel 980, and/or the mesa supportmaterial 971 of the sides and/or top of mesa 970. One or more layers,e.g., a thermal absorber layer, can be optionally disposed over layer911 in the channel 980 and/over the channel walls 970 a, 975 a. In someembodiments, one or more of the layers 912, 913, 915 of the ejectorlayer 910 may be patterned on the ejector 901 region and region 951 asshown in FIG. 9C.

The channels 980 are arranged to carry the ejectable material 966 to theejectors 901. To fill the ejectors, the ejectable material 966 can becaused to flow through vias 955 to the channels 980 and over the ejectorsurface of the ejector layer 910 and subsequently to recede, leavingdroplets 965 of the ejectable material 966 preferentially adhering tothe ejector surface of the ejector layer 910. An aperture structure 990that at least partially covers the channels 980 may be used tofacilitate retention of the ejectable material 966 in the channels 980during the filling process.

FIGS. 10A through 10I illustrate a process for making ejector devicesdiscussed herein in accordance with some embodiments. FIG. 10A shows asubstrate, e.g., silica 1050 having an unpatterned layer of the mesasupport material 1071 deposited thereon. The mesa support material 1071,e.g., poly silicon, can be patterned using a photolithographic processillustrated in FIGS. 10B through 10E. A photoresist layer 1092 isdeposited (FIG. 10B) on the unpatterned mesa support material 1071 andis developed by radiation through a patterned mask 1093 (FIG. 10C).After the photoresist is developed, the subassembly is exposed to anetchant. If a negative resist is used, the irradiated areas of thephotoresist 1092 are resistant to the etchant and the non-irradiatedareas are etched to form mesas 1070, 1075 topped with photoresist 1092.The photoresist 1092 is stripped away leaving the mesas 1070, 1075 ofsupport material 1071 on the substrate 1050 (FIG. 10D). Alternatively tothe processes of FIGS. 10A through 10D, the mesas 1070, 1075 can bepatterned by deposition through a contact mask or applied by printingsuch as flexography or soft lithography.

The ejector layer 1010, including one or more sublayers, is conformallycoated over the mesas 1070, 1075 (FIG. 10F). According to someimplementations, as shown in FIG. 10G, one or more access vias 1094 areformed through the substrate 1050 to allow etchant access to sacrificialmesa 1075 through the substrate. For example, in some implementations,one via is used for each ejector formed. Alternatively, the sacrificialmaterial 1071 of mesa 1075 may be etched from ends of the mesa 1075opened by a photolithographic process or mechanical removal. Thesubassembly is exposed to an etchant which etches the mesa supportmaterial 1071 of mesa 1075 forming one or more hollow area(s) 1025 (FIG.10H). The etchant access via 1094 through the substrate 1050 may beclosed. Alternatively, if the substrate material is opaque to theactivation radiation, the vias may be left open and used as an opticalpathway allowing the activation radiation to heat the ejector layer. Oneor more vias 1055 are formed through the substrate 1050 to fluidicallycouple the channels with a reservoir or other structure configured tocontain the ejectable material (FIG. 10I).

In some implementations, two layers of sacrificial material are used toform the ejector layer. Each of the layers may have different etchingproperties and/or may be etched by different etchants. The use of twosacrificial layers allows the surface of the ejector layer to be formedin more complex shapes. FIG. 11A shows first and second layers 1171,1172 of sacrificial material deposited on a substrate 1150. The firstlayer 1171 and the second layer 1172 of sacrificial material are etchedinto patterned features, for example, by standard photolithographicprocesses (FIG. 11B). In some embodiments the patterned features 1173comprise one or more hemispherical caps. The ejector layer 1110 isconformally coated over the patterned features and the first layer 1173,1171 (FIG. 11C). The first then second layers are etched to form theejector mesa 1175 (FIG. 11D) that includes an ejector layer 1110spanning a hollow area 1125 and having the surface features provided bythe pattern of the second layer of sacrificial material.

FIGS. 12A-121 illustrate a method for making an ejector device having aconvex ejector layer that can be formed with zero stress in accordancewith some embodiments. FIG. 12A shows a substrate 1250 having anunpatterned layer of the mesa support material 1271 deposited thereon.The mesa support material 1271 can be patterned using aphotolithographic process illustrated in FIGS. 12B through 12D. Aphotoresist layer 1292 is deposited (FIG. 12B) on the unpatterned mesasupport material 1271 and is developed by radiation through a patternedmask 1023 (FIG. 12C). After the photoresist is developed, thesubassembly is exposed to an etchant. The irradiated areas of thephotoresist 1292 are resistant to the etchant and the non-irradiatedareas are etched to form mesas 1270 and sacrificial mesa 1275 toppedwith photoresist 1292 The photoresist 1292 is stripped away leaving themesas 1270, 1275 of support material 1271 on the substrate 1250 (FIG.12D). Alternatively to the processes of FIGS. 12A through 12D, the mesas1270, 1275 can be patterned by deposition through a contact mask.

A pin hole is opened in the photoresist that covers the top of thesacrificial mesa 1275 (FIG. 12E). The top of the sacrificial mesa 1275is exposed to an etchant through the pinhole for a sufficient amounttime to produce a convex surface at the top of the sacrificial mesa 1275(FIG. 12F). The photoresist is then stripped away (FIG. 12G) and thesubassembly is conformally coated with the ejector layer (FIG. 12H). Thesacrificial material 1271 of mesa 1275 is etched, e.g., from open endsof the mesa 1275 or through one or more vias in the substrate. Theresulting ejector mesa 1275 includes a convexly shaped ejector layer1210 (FIG. 12I).

FIG. 13 is a block diagram of an ejector system 1300. The system 1300includes an ejector device 1305, e.g., as previously discussed, thatincludes at least one ejector configured to eject droplets of anejectable material when the ejector is heated by a radiation from anactivation radiation source 1310 such as a source of laser light. Theejector device 1305 includes an ejector layer that is configured tothermally expand without phase transition in response to heating by theactivation radiation. The thermal expansion of the ejector layer causesejection of droplets 1350 from the ejector layer. The ejectable materialis contained in a reservoir 1321 or other structure that is fluidicallycoupled to channels of the ejector device 1305. The reservoir 1321 ispart of a fluidic subsystem that may additionally include one or moremanifold(s), pump(s) and/or other fluidic components configured to movethe ejectable material to the ejectors. For example, the fluidicsubsystem may include one or more pump(s) configured to apply positiveand/or negative pressure to the ejector material to charge the ejectorswith droplets of ejectable material. The pump(s) may apply a positivepressure to pressurize the ejectable material, causing the ejectablematerial to flow in the channels of the ejector device and over the freesurface of the ejectors. The pump(s) may apply negative pressure todepressurize the ejectable material, causing the ejectable material torecede from the channels leaving droplets of ejectable materialpreferentially adhering to the free surface of the ejectors.

Movement subsystem 1340 is a structure that allows the ejector device tomove linearly in one, two, or three dimensions along x, y, and/or z axesand/or to rotate around x, y, and/or z axes. Operation of the movementsubsystem 1330, radiation source 1310, and fluidic subsystem 1320 arecontrolled by an electronic control system 1340 which may include amicroprocessor implementing program instructions stored in memory. Underprogram control, the ejector system 1300 may be configured to producethree dimensional objects by ejecting layer after layer of the ejectablematerial according to a predetermined pattern. The pattern may bedigitally stored and accessed by the electronic control system 1340.

FIG. 14 is a flow diagram illustrating a method of using the ejectordevice and/or system discussed above. A droplet of ejectable material isdisposed 1410 on an ejector surface of an ejector layer. The ejectorlayer is heated 1420 by activation radiation such as by absorption of alaser pulse. The heating causes the ejector layer to thermally expandwithout phase transition. In response to the thermal expansion of theejector layer, the droplet of material is ejected 1430 from the ejectorsurface. The ejector device may be moved 1440 along and/or around x, y,and/or z axes to form one or more layers of a 2D or 3D object.

Embodiments discussed herein involve fabrication of a structure which isheated by laser pulse absorption and driven to deform due to thermalstresses at a rate high enough to eject a layer of ink. Using a bimorphor multimorph ejector layer can facilitate buckling above a stressthreshold with predetermined directionality. Motion during buckling canbe much faster than the average rate of change of the stress, therebyeffectively increasing the momentum transfer to the ejectable material.

In some configurations, the ejector device can be fabricated usingphotolithography optionally using at least one layer of sacrificialmaterial. In some configurations, two or more layers of sacrificialmaterial with different etching properties can be used for more complexejector layer shapes. For example, a sacrificial mesa can be createdwith various structures such as hemispherical caps along the length ofthe mesa. Fabrication of the ejector device can involve deposition andpatterning of the one or more sacrificial layers on a radiationtransparent substrate such as glass. Alternatively the mesas can bedeposited through a contact mask. After patterning of the mesas, aconformal transparent layer can be deposited followed by a highlyabsorbing layer to form a bimorph, or in some implementations, just theabsorbing layer is deposited if a non-buckling ejector layer providessufficient ink acceleration. In the bimorph embodiment, the absorbinglayer should also have a higher thermal expansion coefficient than thatof the transparent layer. Various parameters, such as layer/sublayerthicknesses, layer stiffnesses, etc. can be selected to provide aspecified momentum transferable to an overlying bio-ink droplet. Thesurface energy of the top layer of the ejector layer, either theabsorbing sublayer itself or a third sublayer (such as silicone) may bechosen to provide a specified surface energy to bind the ink droplet tothe ejector surface of the ejector layer.

In a subsequent processing step an aperture structure can be attached tothe tops of some of the mesas so that the aperture structures overhangpartially the spaces on both sides of these mesas. The aperturestructures are used in operation to confine the ink. Either before orafter fabrication of the aperture structures, the sacrificial materialwithin the ejector mesa can be etched away, e.g., either from the endsof the ejector mesas or through vias formed in the substrate. Theejector mesa so formed is able to provide multiple thermo-expansiveand/or buckling ink ejectors.

In some embodiments, the ejector mesa which includes one or more hollowareas can be fabricated with solid neighboring mesas. The solidneighbors act as anchors to stiffen the buckling or distortingstructures. In some embodiments, a thermally conductive layer can bedeposited, for example, along the bottom of the ink channel (andoptionally partially or fully up the side wall of the mesas) tofacilitate heat removal and spreading from the illuminated ejectors.

In operation, ink is first pressurized to overtop the ejector mesa thendepressurized to leave behind an isolated top coat of ink (droplet) onthe ejector mesa. Light is focused onto the absorbing layer of a givenejector, inducing heating, thermal expansion and buckling of the localbimorph or thermal expansion defined by a built-in convexity.

Systems, devices, and/or methods disclosed herein may include one ormore of the features, structures, processes, or combinations thereofdescribed herein. For example, a device or method may be implemented toinclude one or more of the features and/or processes described herein.It is intended that such device or method need not include all of thefeatures and/or processes described herein, but may be implemented toinclude selected features and/or processes that provide usefulstructures and/or functionality.

In the above detailed description, numeric values and ranges areprovided for various aspects of the implementations described. Thesevalues and ranges are to be treated as examples only, and are notintended to limit the scope of the claims. For example, embodimentsdescribed in this disclosure can be practiced throughout the disclosednumerical ranges. In addition, a number of materials are identified assuitable for various implementations. These materials are to be treatedas exemplary, and are not intended to limit the scope of the claims.

The foregoing description of various embodiments has been presented forthe purposes of illustration and description and not limitation. Theembodiments disclosed are not intended to be exhaustive or to limit thepossible implementations to the embodiments disclosed. Manymodifications and variations are possible in light of the aboveteaching.

1. A system, comprising: an ejector device including one or moreejectors, each ejector comprising: a substrate; an ejector layer havinga first surface disposed proximate to the substrate and a second surfacearranged to receive a viscous material, the ejector layer configured tothermally expand without phase transition in response to heating byactivation radiation, wherein thermal expansion of the ejector layercauses ejection of the droplet from the second surface of the ejectorlayer towards a media surface; and at least one channel configured tocarry the viscous material to the ejectors; a radiation sourceconfigured to provide the activation radiation to the one or moreejectors; a fluidics subsystem configured to carry the material to theat least one channel; and a transport subsystem configured to providerelative movement between the ejector device and the media surface. 2.The system of claim 1, wherein the ejector layer comprises multiplelayers including a first layer having a first coefficient of the thermalexpansion, CTE1, and a second layer having a second coefficient ofthermal expansion, CTE2, wherein CTE2>CTE1.
 3. The system of claim 1,wherein the viscous material has viscosity in a range of about 20 andabout 50,000 centipoise.
 4. The system of claim 1, wherein the one ormore ejectors comprise an array of ejectors.
 5. The system of claim 4,wherein the array is a one dimensional array that includes one or morehollow mesas.
 6. The system of claim 4, wherein the array is a twodimensional array that includes one or more hollow islands.
 7. Thesystem of claim 1, further comprising: one or more mesas disposed on thesubstrate, at least one of the mesas being an ejector mesa comprisingthe ejector layer that spans the hollow area; and wherein the at leastone channel is disposed adjacent to at least one of the one or moremesas.
 8. The system of claim 1, wherein the substrate comprises atleast one of: a material that is transparent at wavelengths of theactivation radiation; and one or more vias through the substrate.
 9. Thesystem of claim 1, wherein the one or more ejectors comprise one or morehollow mesas, each of the one or more hollow mesas disposed between andbonded to solid mesas.
 10. The system of claim 9, wherein the ejectorlayer includes at least one layer that conforms to the channel and wallsof the solid mesas.
 11. The system of claim 1, further comprising athermally conductive layer disposed at least partially along thechannel.
 12. The system of claim 1, wherein the substrate includes viasfluidically coupled to the channel.
 13. The system of claim 1, furthercomprising an aperture layer disposed at least partially over thechannel.
 14. The system of claim 1, wherein the absorption of theactivation radiation in the second layer causes buckling of the ejectorlayer.
 15. The system of claim 1, wherein the second layer comprisesamorphous Ge or amorphous Si.
 16. The system of claim 1, wherein atleast one layer of the ejector layer comprises a binding materialconfigured to provide a predetermined surface energy.
 17. The system ofclaim 1, wherein a portion of the ejector layer, when unheated, isconvex and bends toward the substrate.
 18. The system of claim 1,wherein the ejector layer has a built in stress gradient.
 19. A system,comprising: an ejector device including one or more ejectors, eachejector comprising: a substrate; an ejector layer having a first surfacedisposed proximate to the substrate and a second surface arranged toreceive a viscous material, the ejector layer configured to thermallyexpand without phase transition in response to heating by activationradiation, wherein thermal expansion of the ejector layer causesejection of the droplet from the second surface of the ejector layertowards a media surface, the ejector layer comprising multiple layersincluding a first layer having a first coefficient of the thermalexpansion, CTE1, and a second layer having a second coefficient ofthermal expansion, CTE2, wherein CTE2>CTE1; and at least one channelconfigured to carry the viscous material to the ejectors; a radiationsource configured to provide the activation radiation to the one or moreejectors; a fluidics subsystem configured to carry the material to theat least one channel; and a transport subsystem configured to providerelative movement between the ejector device and the media surface. 20.The system of claim 19, wherein the viscous material has viscosity in arange of about 20 and about 50,000 centipoise.